1Radiology, Mayo Clinic, Rochester, MN,
United States; 2Philips Healthcare, Highland Heights, OH, United
States; 3Boston University School of Medicine, Boston, MA, United
States

During
the Alzheimers Disease Neuroimaging Initiative (ADNI) multicenter study, a
laser alignment light was mis-calibrated on one scanner, leading to a
displacement error in the isocenter location used during image
reconstruction. Consequently, the standard gradient distortion correction was
inaccurate and the resulting data were unusable for longitudinally tracking
brain changes. Off-line processing was used to remove the aberrant distortion
correction from ADNI phantom data, then those images were shifted by a
variable displacement, and finally the images were re-corrected for gradient
distortion. The actual displacement error was determined by this method and
the subject data could be re-corrected and salvaged.